The present invention relates to a pipe joint which is used so as to be attached to a pipe end of a spiral corrugated pipe, and particularly relates to a pipe joint which is preferably used so as to be attached to a pipe end of a synthetic resin pipe having a spiral corrugated outer circumferential surface and having a pipe wall with reinforcing yarn buried therein.
A conventional technique for connecting synthetic resin spiral corrugated pipes of this type is as follows. In a place where such spiral corrugated pipes were used, pipe ends of two spiral corrugated pipes were inserted into a cylindrical pipe joint from opposite sides of the joint so as to make the pipe ends abut on each other. Sealing means were applied to the spiral corrugated pipes respectively before or after the insertion of the pipes. Thus, the two spiral corrugated pipes were connected to or coupled with each other.
Another conventional technique is as follows. As shown in FIGS. 7 and 8, a nipple J having a simple tubular end portion widened so as to be shaped like a trumpet was forced into a pipe end of a synthetic resin spiral corrugated pipe P. Then, a thick wire member 2 was wound on a trough portion of an outer circumferential portion of the pipe by one and a half turns. Then, ends of the wire member 2 were compressively tightened by nuts 3 through a saddle metal member 1.
Connection of spiral corrugated pipes of this type had to be made at a site of the pipe laying-out which was not always in a desirable environment and by a worker who was not always a skilled or professional worker while being influenced by atmospheric temperature and weather. Particularly the former conventional technique had a problem that a connection could not be made speedily because a great deal of time and labor were required. Further, in each of the two conventional techniques, not only water leakage occurred easily as the internal pressure of the pipe increased even in the case where sufficient connecting work was performed, but also such an accident of metal fitting""s falling out of the pipe occurred frequently before the internal pressure of the pipe reaches a critical pressure of the pipe.
Particularly in the case where the pipe used herein was a pipe having a large number of reinforcing yarn members y in its pipe wall as represented by a synthetic resin pipe P shown in FIGS. 1 and 6, even if the connection of the joint to the pipe looked sufficient from external appearance, respective cut ends of the reinforcing yarn members y at a cut end of the pipe were moved successively so as to be pulled into the longitudinal inner deeper side of the pipe by the repetition of expanding and meandering operations which occurred in the pipe whenever a large amount of water or air pressure was applied to the inside of the pipe. Accordingly, a portion near the cut end of the pipe was provided as a region which contained a resin material alone so that the reinforcing yarn members y were absent from the region. As a result, the strength of the coupling portion between the pipe and the joint was lowered. This was a cause of water leakage and further a factor leading to an explosion of the pipe.
Therefore, it is an object of the present invention to solve the aforementioned problems in the conventional pipe joint. In particular, it is an object of the present invention to provide a pipe joint which can be connected to a pipe end of a synthetic resin spiral corrugated pipe in a factory by a skilled worker in advance and which can be surely and easily connected to a pipe end even at a pipe laying-out site. Thus, pipes can be connected with each other easily and speedily.
Further, the reinforcing yarn members y can be sufficiently prevented from moving from a cut end portion of a pipe toward a longitudinally inner deeper side of the pipe even if the pipe contains a large number of reinforcing yarn members y in its pipe wall. Accordingly, the strength at the cut end portion of the pipe can be prevented from being lowered. Thus, the pipe joint can be connected to the pipe in such a state that neither water leakage nor pipe explosion occurs easily.
The above object according to the present invention can be achieved by a pipe-end-connecting joint connected to a pipe end of a synthetic resin pipe P formed so as to have a spiral corrugated outer circumferential surface and have a pipe wall with reinforcing yarn buried therein, the joint comprising a nipple inserted in the pipe end, a holder for tightening the outer circumference of the pipe end, and an elastic packing divided into half parts and attached in the holder. The nipple includes a tubular portion provided in one longitudinal end side thereof so as to be inserted in the pipe end, a connection portion provided in the other longitudinal end side thereof so as to be connected to another joint, and a flange portion provided in a longitudinal intermediate portion thereof so as to protrude outward. The holder is divided longitudinally into two split parts so that each of the two split parts has a semicircularly formed inner circumferential surface. Each of the two split parts has one longitudinal end side in which one of the half parts of the elastic packing is mounted, and has the other longitudinal end side in which a ring-like groove is formed so as to be fitted to the flange portion, and further has a longitudinally intermediate portion between the one and the other longitudinal end sides in which a spiral corrugated portion is formed along the outer circumferential surface of the pipe. The spiral corrugated portion having a spiral protruding portion an inner diameter of which is smaller than an outer diameter of a, trough portion r of the pipe when the nipple is inserted in the synthetic resin pipe P.
In the above-mentioned joint, the two split parts preferably have holes for insertion of connection bolts.
In the above-mentioned joint, it is advantageous that the elastic packing is configured so as to be divided into half parts each having an inner surface shaped like a semicircular arc in the same manner as the holder. The inner circumferential surface of the elastic packing is shaped like a spiral uneven surface which is substantially the same as the spiral uneven shape of the outer circumferential surface of the pipe P. That is, the elastic packing is formed so as to adhere closely to the outer circumferential portion of the pipe P without any gap, or at least an inner circumferential surface portion of the elastic packing is formed from an elastically deformable material. For example, the elastic packing is preferably formed from a natural rubber material or a synthetic rubber material.
The material for the half split joint used in the present invention is not limited specifically. For example, a hard thermoplastic synthetic resin material such as hard polyethylene, hard polypropylene, or the like, may be preferably used because the material has weather resistance. Alternatively, the joint may be made from a thermosetting resin. Further, the material is not limited to the synthetic resin material. The present invention can be also be achieved by an FRP resin in which glass fiber is mixed with resin or by a structure in which an iron plate is embedded in a thick layer. The joint made from only the synthetic resin material is, however, preferable in terms of light weight.